As one type of engines, a gas engine is known which is operated by combusting gaseous fuel (fuel gas) such as natural gas, town gas, and the like. This gas engine can achieve high efficiency and high output performance. Therefore, the gas engine is widely used for mainly regular/emergency power generating engines, construction machinery engines, and engines mounted on ships, railway vehicles, and the like.
A gas engine is known in which a cylinder head includes a prechamber for ignition. In this gas engine, an air-fuel mixture obtained by mixing fuel gas and air is supplied to a main combustion chamber inside the cylinder head. In addition, the fuel gas is also supplied to the prechamber. Then, if a piston inside the main combustion chamber moves close to the compression top dead center and the fuel gas inside the main combustion chamber is compressed, the fuel gas supplied into the prechamber is ignited by an ignition plug included in the prechamber. This generates a flame from the prechamber, and the flame is injected into the main combustion chamber through a cap disposed in the prechamber. In this case, the flame ignites the air-fuel mixture inside the main combustion chamber, thereby allowing the gas engine to perform a combustion operation (for example, Patent Document 1).
Here, the prechamber is configured to include the cap that supplies the flame into the main combustion chamber, and a prechamber holder that forms the prechamber into which the fuel gas is supplied.
According to the configuration disclosed in Patent Document 1, the prechamber holder (laser ignition plug) is attached to a cylinder head by screwing a male screw formed on an outer peripheral surface of the prechamber holder into a female screw hole formed in the cylinder head. The cap (prechamber module) and the prechamber holder are attached to each other by screwing a male screw formed on an outer peripheral surface of the cap into a female screw hole of a cap attachment portion formed on the prechamber holder side.